Harry it's based on population density and regional factors. I live in the Valley of the sun, keyword Valley. Its a great place to be from,I have seen pollution steadily rise thoughout my 48 years of being here, we used to have beautiful skies, open land, Now we have a brown cloud over us, and lots of cars,and construction.The only times We see a true blue sky is when you go out of town, or when it rains. If it happens to rain, you end up fighting your Allergies. Which is kind of Ironic, since this used to be the place where people would come to for Asthma relief. I don't think Emission testing is a Joke. Especially when my wife has an asthma attack.